1. Field of the Invention
This invention relates to a layout of a fuse integrally formed on a substrate with elements of a semiconductor device and a method of trimming.
2. Description of the Related Art
A fuse simultaneously formed with elements of a semiconductor device is used upon trimming for adjusting characteristics of the elements. Especially, in recent years, the fuse is used in a redundant circuit of a memory device to switch to a row or column of a spare circuit when a certain row or column of a main circuit is defective, thereby increasing production yield.
The fuse is not formed by individual process but generally formed with main elements in the process of producing electrodes of the semiconductor device. A fusion-type metal is usually used for the fuse, wherein the metal is cut or disconnected by drawing current or applying laser beam to the narrow portion of the metal. A short-circuited type fuse is also used, which has a capacitor structure where an insulating film is sandwiched by metals and broken down by application of voltage to make short-circuited between the metals.
The main stream of the conventional method has been using a single layer metal, such as aluminum (Al) and Copper (Cu), for electrode wiring of the semiconductor device. However, as the fine structure is required, in case of Al wiring, a two-layer electrode has become popular, wherein a conventional.wiring metal is formed on a thin lower layer made of a barrier metal, such as tungsten (W), titanium (Ti), and titanium nitride (TiN).
Japanese Patent Application Kokai Number 9-36234 discloses the structure of the fuse and manufacturing method thereof.
In the conventional method of cutting the fusion-type fuse by drawing current, it was easy to cut the electrode wiring made of the single layer of Al. However, when the electrode has the two-layer structure including the lower layer of the barrier metal, although the main wiring metal of the upper layer is easily cut, the thin barrier metal is prone not to be completely cut because the barrier metal has a relatively high resistance which does not permit large current to be drawn to the barrier metal.
It is difficult to apply higher voltage between the fuses due to adverse influences on the elements. Thus, when the barrier metal is not cut completely and remains, it causes a characteristic failure and a leakage problem, resulting in decrease of the yield and reliability.
When the fuse is cut by applying laser beam, there is no problem caused by the two-layer structure of electrode. However, if the irradiation of laser beam is not accurate, the fuse is not cut completely and some metal remains at an end of the fuse, resulting in decrease of the yield and reliability because the irradiation of laser beam cannot be repeated at the same position.